None.
Not Applicable.
The present invention relates generally to a laser transmitter and, more particularly, to a laser reference system and method of orienting a reference plane of laser light generated by a laser transmitter. The laser transmitter is effectively aligned so that the laser transmitter defines a plane having desired slopes in a desired alignment direction and in a direction perpendicular thereto.
Laser light systems have been employed in numerous prior art surveying and construction applications. In one type of system, a laser light transmitting device provides a rotating laser beam which establishes a reference plane. Typically, the reference plane creates either a constant horizontal bench mark of elevation, or an appropriately tilted reference over a work site. The laser light is either detected by the naked eye or by one or more laser beam detectors, placed at considerable distances from the transmitting device or mounted on construction equipment that is operated at the work site.
Prior to operation, it is necessary to set up the transmitting device at the work site in proper orientation to the work site. As an example, assume that an architect has previously determined that the work site is to slope in a certain direction at a certain grade. Assume further that the work site is rectangular, and that a corner of the work site is selected as the origin of a coordinate system, with one edge of the rectangle being the x-axis and the other edge of the rectangle being the y-axis. The desired fall line may extend in a direction between the x-axis and y-axis. The architect will have specified an x-axis slope and a y-axis slope for the work site that together produce the desired slope along the fall line.
The transmitter is placed at the corner of the work site that constitutes the origin. The transmitter has its own internal x-axis and y-axis, and these are marked on the top of the transmitter. The operator manually lines up the transmitter x and y axes with the work site x and y axes using the markings, or using a telescope that may be mounted on the top of the device for this purpose. Neither of these arrangements for aligning a transmitter permit great precision
If the transmitter were to be perfectly aligned such that its x-axis and its y-axis were parallel to the x-axis and y-axis of the work site, respectively, then when the operator inputted the x-axis grade and the y-axis grade, the transmitter would produce a reference plane of light having the correct pitch along the fall line. A problem develops, however, when the x-axis and the y-axis of the transmitter are misaligned, i.e., pivoted slightly clockwise or counterclockwise, as seen from above, with respect to the x-axis and y-axis of the work site. If the transmitter is misaligned and if the operator inputs the desired work site axes slopes, the transmitter will produce a reference light plane having the correct pitch, but the maximum pitch of the reference plane will not be aligned with the desired fall line. Instead, the reference plane will be rotated slightly about a vertical axis from the orientation that is desired.
The present invention determines the amount of that misalignment about a vertical axis (termed xe2x80x9cthe rake anglexe2x80x9d) and then compensates for it. Stated another way, the grade rake angle is the angular misalignment (as seen from above) of the x and y axes of the transmitter, and the x and y axes of the work site, respectively. The present invention determines this rake angle and alters the operation of the transmitter such that a properly oriented reference plane is produced.
One system for aligning a transmitter to a work site is shown in U.S. Pat. No. 6,055,046, issued Apr. 25, 2000, to Cain, and assigned to the assignee of the present invention. The Cain patent discloses a transmitter that includes an angle encoder. The angle encoder continuously indicates the angular orientation of the rotating beam. The transmitter and a retroreflective target are positioned along a side of the work site, spaced apart in the direction to which the laser transmitter is to be aligned. The angular orientation of the target is then determined by the angle encoder output when light is reflected from the target back to the transmitter. Alternatively, as shown in the Cain patent, an electro-optical detector may be used with the detector, sending a signal via a radio or other transmitter back to a receiver on the transmitter when the beam is detected. In either event, the transmitter axes are rotated into alignment electronically. This arrangement requires an accurate angle encoder, thus adding to the expense and complication in the construction of the device.
Accordingly, it is seen that there is a need for an improved and simplified system for aligning a laser transmitter to a work site, such that a plane of laser light projected from the laser transmitter accurately defines a reference plane with a properly oriented slope.
This need is met by a laser reference system according to the present invention, which includes a laser transmitter, a detector, and a processor. The transmitter has an optical system that is arranged to generate a laser beam. The optical system projecting the laser beam radially along a rotational arc defined about a central rotational axis, thereby substantially defining a reference plane of laser light; and a positioning arrangement, coupled to the optical system, for adjusting an angular orientation of the optical system with respect to a first transmitter axis and with respect to a second transmitter axis. The detector is arranged to detect reception of the laser beam, and generally includes a vertically arranged row of detector elements, and a transmitter for transmitting information regarding the location of the laser beam, as detected by the detector elements. A processor is adapted to receive the transmitted information from the detector regarding the location of the laser beam. The processor is arranged to determine the distance in an alignment direction from the transmitter to the detector, determine the distance from the detector to the first transmitter axis in a direction generally perpendicular to the alignment direction, and calculate the rake angle between the first transmitter axis and the alignment direction. The rake angle is calculated as the arctangent of the ratio of the distance from the detector to the first transmitter axis in a direction generally perpendicular to the alignment direction, to the distance in an alignment direction from the transmitter to the detector.
The transmitter includes an input for inputting a first desired slope for the reference plane of laser light in the alignment direction and a second desired slope in a direction perpendicular thereto. The processor is further adapted to calculate a first calculated slope and a second calculated slope based on the calculated rake angle.
The processor determines the distance in the alignment direction between the transmitter and the detector by directing the beam in succession to illuminate two detector elements spaced vertically along the row, determining the included vertical angle of the reference plane as it shifts from illuminating one of the two detector elements to illuminating the other of the two detector elements, and computing the distance from the transmitter to the detector based on the height difference between the two detector elements and the included vertical angle.
The processor is adapted to determine the distance from the detector to the first transmitter axis in a direction generally perpendicular to the alignment direction by the steps of illuminating the center of the row of elements with the reference plane horizontal in the direction of the second transmitter axis, tilting the reference plane in the direction of the second transmitter axis until a detector element, vertically displaced from the center of the row of elements, is illuminated, determining the angle by which the reference plane is tilted in the direction of the second transmitter axis, and computing the distance from the detector to the first transmitter axis in a direction generally perpendicular to the alignment direction based on the height difference between the center of the row of elements and detector element that is vertically displaced from the center of the row of elements, and on the angle by which the reference plane is tilted.
A method according to the present invention of orienting a reference plane of laser light generated by a transmitter, the transmitter including a positioning arrangement that adjusts the angular orientation of the reference plane with respect to a first transmitter axis and with respect to a second transmitter axis perpendicular thereto, the laser light being detected along a generally vertical detector line defined by a detector, with the detector also including a transmitter that transmits information regarding the location of the laser light, comprises the steps of: determining the distance in an alignment direction from the transmitter to the detector; determining the distance from the detector to the first transmitter axis in a direction generally perpendicular to the alignment direction; and calculating the rake angle between the first transmitter axis and the alignment direction.
The step of determining the distance in an alignment direction from the transmitter to the detector may comprise the steps of directing the light in succession to illuminate two points spaced vertically along the detector line, determining the included vertical angle of the reference plane as it shifts from illuminating one of the two points to illuminating the other of the two points, and computing the distance from the transmitter to the detector based on the height difference between the two points and the included vertical angle.
The step of determining the distance from the detector to the first transmitter axis in a direction generally perpendicular to the alignment direction may comprise the steps of: illuminating the center of the detector line with the reference plane horizontal in the direction of the second transmitter axis; tilting the reference plane in the direction of the second transmitter axis until a point on the detector line, vertically displaced from the center of the detector line, is illuminated; determining the angle by which the reference plane is tilted in the direction of the second transmitter axis; and computing the distance from the detector to the first transmitter axis in a direction generally perpendicular to the alignment direction based on the height difference between the center of the detector line and the point on the detector line that is vertically displaced from the center of the detector line, and on the angle by which the reference plane is tilted. The step of calculating the rake angle between the first transmitter axis and the alignment direction may comprise the step of determining the arctangent of the ratio of the distance from the detector to the first transmitter axis in a direction generally perpendicular to the alignment direction to the distance in an alignment direction between the transmitter and the detector.
Alternatively, a method of orienting a reference plane of laser light generated by a transmitter, the transmitter including a positioning arrangement that adjusts the angular orientation of the reference plane with respect to a first transmitter axis and with respect to a second transmitter axis perpendicular thereto, the laser light being detected along a generally vertical detector line defined by a detector, with the detector also including a transmitter that transmits information regarding the location of the laser light, includes the steps of: defining an alignment direction from the transmitter by positioning a detector in the alignment direction for illumination with the plane of laser light; tilting the reference plane in a direction of the first transmitter axis while keeping the plane horizontal in a direction of the second transmitter axis; effectively rotating the plane of laser light such that a predetermined point on the detector line is illuminated at two effective angular positions of rotation of the plane; determining a mid-point between the two effective angular positions as the first transmitter axis, and determining an angular position at ninety degrees thereto as the second transmitter axis; determining the angular difference between the alignment direction and the first transmitter axis as a rake angle; and orienting the reference plane with respect to the first and second transmitter axes such that a desired orientation with respect to the alignment direction and a direction perpendicular thereto is achieved.
As another alternative, a method of orienting a reference plane of laser light may comprise the steps of: defining an alignment direction from the transmitter by positioning a detector in the alignment direction for illumination with the plane of laser light; tilting the reference plane and determining a grade x1 in a direction of the first transmitter axis and a grade y1 in a direction of the second transmitter axis which cause a point on the generally vertical detector line to be illuminated; tilting the reference plane and determining a grade x2 in a direction of the first transmitter axis and a grade y2 in a direction of the second transmitter axis which cause a point on the generally vertical detector line to be illuminated; calculating the rake angle between the first transmitter axis and the alignment direction; and orienting the reference plane with respect to the first and second transmitter axes such that a desired orientation with respect to the alignment direction and a direction perpendicular thereto is achieved.
The step of calculating the rake angle xcex8 between the first transmitter axis and the alignment direction includes the step of calculating the rake angle according to the equation:
xcex8=arctan((y1xe2x88x92y2)/(x1xe2x88x92x2). 
Alternatively, this may be calculated according to the equation:
xcex8=arctan(xe2x88x92(x1xe2x88x92x2)/(y1xe2x88x92y2)). 
The step of orienting the reference plane with respect to the first and second transmitter axes such that a desired orientation with respect to the alignment direction and a direction perpendicular thereto is achieved, may comprise the step of orienting the reference plane with respect to the first and second transmitter axes according to the equations:
x=xxe2x80x2 cos(xcex8)xe2x88x92yxe2x80x2 sin(xcex8), and y=xxe2x80x2 sin(xcex8)+yxe2x80x2 cos(xcex8). 
In these equations, xxe2x80x2 and yxe2x80x2 represent the desired grades in the alignment direction and a direction perpendicular thereto, and x and y represent the grades in the first and second transmitter axes.
Accordingly, it is an object of the present invention to provide a laser transmitter that produces a plane of laser light having a first desired slope in an alignment direction and a second desired slope in a direction perpendicular thereto; and to provide a laser transmitter in which the grade rake angle is determined and compensation for the grade rake angle provided.